Method for making bandage material for orthopedic casts and product thereof



METHOD FOR MAKKNG ing immobilizing or support.

Unite ttes aten BANDAGE MATERIAL FOR ORTHOPEDIC CASTS AND PRUDUCTTHEREGF No Drawing. Application January 21,

Serial No. 4055M;

8 Claims. (Cl. 128-431) This invention relates to cast-forming elementsdesigned to be used for immobilizing or supporting parts of the body.

In conventional practice cast-forming elements composed of plaster ofParis or other settable material supported on suitable backing materialare utilized in making casts that fit closely to the part of the bodyrequir- The backing material is most usually in strip form wound into aroll or suitably pre-cut to the desired shape as, for instance, inmanufacture of arm splints. The backing material may be woven gauze orcrinoline of suitable mesh, or may be of knitted construction. In use,the cast-forming element, such as a bandage, may be immersed in water,excess water squeezed out by hand pressure, anclthe bandage then appliedto the body in spiral fashion until enough thickness has been built upto provide the cast strength needed. 7

One technique of applying the plaster of Paris to the backing involvespassing the backing fabric through a chamber in which the plaster ofParis, in the form of a fine powder, is dusted or otherwise coated onthe backing. This is a dry operation, and the product is commonly knownas looseplaster bandage." The loose plaster bandage has markeddisadvantages. The plaster is not firmly secured to the backingand'tends to drop off in'handling and wash oif during immersion of thebandage prior to application by the physician. This loss of plasterresults in the production of casts of non-uniform and generally lowstrength.

The patent faults of the loose plaster bandage gave rise toinvestigation into ways of improving adherence and minimizing loss ofplaster of Paris from the backing material. The result of thesedevelopments was the hardcoated bandage in which the plaster of Paris ismixed with a liquid-dispersing medium into the paste or slurry, and thispaste is' employed to impregnate the backing sheet. Upon drying of theplaste-impregnated backing one obtains a plaster of Paris bandage inwhich the plaster of Paris is bonded to the fabric, i. e. a hard-coatedbandage. In procedures utilizing Water or aqueous liquids as dispersingmedium for the paste it has been a problem to inhibit setting of theplaster of Paris, i. e. conversion of the hemihydrate to the dihydrateof calcium sulfate, between the time the paste is first prepared and thetime the bandage is dried to produce the finished product. For thispurpose, the use of'various retarders such as ammonium 'borate(disclosed in U. S. P; 2,557,083), or acetic acid has been proposed, orbandages have been prepared by the so-called -hot'water process in whichsetting of the plaster of Paris was prevented or minimized by keepingthe paste hot during the critical period between initial wetting of theplaster and final drying of the bandage.

Plaster of Paris bandages have always had certain inherent disadvantageswhich have long been well recognized by the profession and bythe trade.In'the first place, plaster of Paris has by nature a. high. density As!and is, therefore, a heavy material, which is a considerabledisadvantage for ambulatory patients. Further, in order to assureadequate cast strength, it has been deemed advisable to employ plasterof Paris bandages in considerable thickness, which not only aggravatesthe weight disadvantage, but also decreases X-ray transparency. It wouldbe desirable, if possible, to make a cast so thin that it would bepermeable to X-rays, thereby making possible taking of X-ray pictureswhile the cast is still in place on the body of the patient. Set plasterof Paris casts are also notably susceptible to deterioration uponContact with water. Improvement in water resistance would be ofparticular advantage in cases of incontinent patients, or in the case ofarm casts which are apt to become wetted with water when the hands arebeing washed.

Ordinary plaster of Paris bandages have no inherent resistance to growthor reproduction of microbes. Growth of micro-organisms between the skinand the cast, or within the cast itself, has in many cases createdserious problems, particularly in cases of large body casts or bodyjackets which remain in place for weeks or even months. Growth ofmicro-organisms within the cast may be even more serious in cases wherecasts are placed over open wounds or points of irritation. Hence, itwould be desirable, if feasible, to prepare a cast which possessesinherent anti-microbial properties so as to eliminate or minimize thetendency of microbes to live and reproduce within the cast.

Objects of the invention include improving the strength, lightness andX-ray transparency characteristics of plaster of Paris bandage casts.Another object is to incorporate a strengthening agent in hard-coatedplaster of Paris bandages so as to improve the strength of the castprepared therefrom. Still other objects comprise improving the earlystrength, resistance to deterioration from exposure to water aftersetting, and anti-microbial action of casts prepared from plaster ofParis bandages.

The strength-giving material incorporated in the paste which is employedto impregnate the backing must, of course, be refractory to theretardant employed in cases where an aqueous liquid is utilized in thepaste, and must in any case resist the elfect of the plaster of Parisitself. It must resist deterioration under conditions necessary toeffect removal of liquid, i. e. elevated temperature.

The finished bandage also must have stability so that it may be storedon the shelf of the wholesaler and retailer for a reasonable length oftime without excessive decrease in strength-producing properties. Afurther object of the invention, therefore, is to incorporate astrengthening agent in a hard-coated plaster of Paris bandage, thedesired strengthening agent being refractory to the conditions to whichit is subject, and the finished bandage having a suitable storage life.

The foregoing objects are realized according to the invention in theform of a cast-producing element comprising a supporting fabric havingbonded thereto a composition comprising 5 to 30% by weight of analdehydetriazine resin, and -70% by weight of plaster of Paris based onthe total weight of resin and plaster of Paris. The invention bandage isprepared by making a paste or slurry of a dispersing liquid, plaster ofParis and the. uncured aldehyde-triazine resin, plus a suitable amountof retarder if required, the amount of resin and plaster of Paris beingin the ranges aforesaid, impregnating the backing with'the paste, anddrying the impregnated backing in a time short enough to preventsubstantial curing of the resin and at a temperature high enough toeffect drying of the bandage within the time requirement, but belowtemperature at which substantial curing of the resin would take place.Advantageous properties of the invention bandage include greater caststrength (including superior early strength), resistance to water aftersetting of 3. the cast, resistance to micro-organisms, and otheradvantages suggested by the foregoing recitation of objects. Otherfeatures of the invention and its preferred embodiments are set forthhereinafter.

The triazine-aldehyde resin, the use of which is contemplated accordingto the present invention, is preferably the one prepared from melamine,a species of triazines, with formaldehyde, a particular aldehyde. Thecondensation product of about 1 mol of melamine with about 3 or moremols of formaldehyde is suitable. However. the invention is not limitedto a particular ratio of triazine to aldehyde, nor is it limited to aparticular triazine, melamine, nor the particular aldehyde,formaldehyde. It is, however, preferred according to the invention thatthe triazine-aldehyde resin be water-dispersible, and be enpable ofbeing cured to a hard-set water-insoluble state. The resins are of thetype which are now commercially available, and which are described inUnited States Patent 2,260,239 issued October 21, 1941 to Talbott andUnited States Patent 2,310,004 issued February 2. 1943 to Widmer et al.Alternatively, a suitable resin may be made by mixing about 1 mol ofmelamine with 4 mols of formaldehyde in the form of a 37% aqueoussolution (formalin). The formaldehyde is preferably first brought to apH of 8.84 by addition of 3% aqueous solution of sodium hydroxide. Themixture of melamine and alkalinized formaldehyde is preferably heatedunder a reflux condenser for about 15 minutes, after which time water isremoved overhead from the reaction vessel as the reaction proceeds.Removal of distillate is continued for about 15 minutes and until thetemperature of the reactor charge is about 105 C. At this point theoperation is interrupted and the batch cooled to about 60 C. as rapidlyas possible. The product is a clear. slightly viscous oily-appearingsyrup having a pH of about 8.1 and a resin content of about 50%. It maybe used in preparing pastes of resin-plaster of Paris for impregnatingfabrics to make plaster of Paris bandages according to the presentinvention.

The plaster of Paris used for purposes of present invention may beordinary plaster of Paris of the type conventionally incorporated inplaster of Paris bandages, or may be the high strength type plaster ofParis commonly known as alpha gypsum. The latter material is disclosedand described in U. S. P. 1,901,051, issued March 14. 1933 to Randel andDailey. This high strength gypsum is manufactured by calcination ofgypsum rock in contact with steam at 17 to 20 lbs. gauge pressure.followed by drying and grinding. Alpha gypsum differs from ordinaryplaster of Paris in that its compressive strength will range from 5000lbs. per square inch on upward. Alpha ypsum is further differentiatedfrom ordinary laster of Paris or hemihydrate in the physical nature ofindividual crystal fra ments composing the finely ground product. Ttsproperties and methods employed in production are fully disclosed in theabove-mentioned Randel et al. patent.

Triazine-aldehvde resin is incorporated in the paste or slurrv. andeventually in the completed plaster of Paris bandage. in amountsufiicient to impart to the final product a substantial increase instrength and substantial improvement in properties from the standpointsmentioned in the statement of objects above. Generally. appreciableimprovement in properties may be noted if the amount of resin is atleast about of the total combined weights of resin and plaster of Paris,i. e. 5% resin and 95% plaster of Paris. Optimum properties from thestandpoint of final cast strength, early strength, resistance to water,etc., are noted within the preferred composition to resin, 90 to 85%plaster of Paris by weight. At resin compositions substantially above15% advantages of the invention will still be notable. However, as resinconcentration increases above this value there may be a correspondingincrease in difiiculty of preparing and impregnating the paste on thebacking fabric, and particularly where aqueous pastes are utilized theremay be increased difiiculty in removing water from the impregnatedfabric to produce the desired dry finished bandage. Accordingly, resinconcentrations are generally maintained below about 30% by weight basedon the combined weights of resin and plaster of Paris.

From the standpoint of simplicity of operation and required apparatus itis preferable to employ water as liquid dispersant for the paste orslurry. However, the invention is not limited to a particularpaste-forming liquid. Certain advantages of the invention inhere by useof organic nonaqueous liquids such as isopropyl alcohol, aqueousalcohol, or methylene chloride. In these cases, use of a retarder may bedispensed with since there is not sulficient water in the system to setthe plaster of Paris in the slurry.

As indicated above, the period between paste formation and the finaldrying of the bandage is a critical one in that the plaster of Paris andresin are subjected to conditions which tend to destroy or derogate fromthe soughtfor properties of the bandage. Hence, control of operatingvariables in this period is important. One yarrable to be controlled isthe pH of the paste. pH 18 maintained above about 7.0, and preferably inthe approximate range 7.0 to 10.0, in order to minimize curing of thetriazinealdehyde resin. pH may be controlled by incorporat ng suitableamounts of alkalizing material and by ehmrnatmg any ingredients whichwould tend to lower the pH. Retarders other than the ammonium boratementioned specifically may be employed providing they do not produceundesirably low pH so as to effect advancement or curing of the resin.

Drying, i. e. removal of liquid from the lmpr egnated bandage, whetherit be aqueous or nonaqueous liquid as described above, is carried out attemperature and other conditions which minimize tendency of the resin toadvance or cure. Removal of liquid should be brought about in theminimum time and at the minimum temperature feasible. That is, thedrying conditions should be maintained so that the time required toeffect desired degree of removal of liquid is short enough so thatcuring of the resin is not excessive. Furthermore, during this dryingperiod temperature is maintained below a. level at which appreciablecuring will take place, but sufiiciently high to efiect removal of waterwithin the time limits specified above. Most preferably, temperaturesare maintained at not greater than about 300 F. A suitable operatingrange of temperature for drying aqueous pastes may be found between 200and 300 F.

The reason for the critical nature of the drying period is that liquid,particularly water, tends to promote or catalyze not only setting of theplaster of Paris, i. e. conversion to the dihydrate or gypsum, but alsotends to catalyze advancement or curing of the resin. The resin oncecured, of course, can impart no strengthening characteristics to thecast-forming bandage and, in fact, materially detracts from the strengthproperties that the plaster of Paris would have in the absence of anyresin. Accordingly, drying conditions described above are maintaineduntil free (volatile) water content of the bandage has been reduced tobelow 0.3% based on the weight of resin. Pursuant to maintaining desiredlow water content of the bandage and preventing the bandage, once dried,from absorbing water from the atmosphere, the bandage is most preferablywrapped in a sealed sub stantially water vapor-impermeable wrapper orcontainer promptly after leaving the drying operation. If the bandagematerial is to be slit into widths narrower than the web coated anddried in the bandage-making operation, such slitting will preferably becarried out after drying and before packaging so that the packagedbandage, once sealed, may be maintained intact until finally used by theconsumer.

The resinplaster of Paris bandages of the invention cedure.

may contain conventional amounts "of'plasticizer such as glycerols,glycols, polyglycols, etc. Setting time of the bandage may be controlledby addition of accelerators or retarders known in the art to beeifective for controlling the setting time of the plaster of Paris.Retarders include soluble citrates, phosphates, acetates, or otherorganic retarders. These ingredients, when used, are generallyincorporated into the plaster of Paris-resin paste described above.

Another ingredient employed in preferred embodiments of the invention isa binder which serves the purpose of elfecting maximum adhesion of theplaster of Paris and resin to the bandage backing material. Suitablebinders are polyvinyl acetate emulsions, described in U. S. P.2,655,148. Other usable binders include emulsions or solutions ofpolymers of vinyl chloride, vinyl acetate, acrylates, methacrylates, orbutadiene; or copolymers, interpolymers or polymeric mixtures thereof.The binder is preferably mixed into the paste just as are the othercomponents of the bandage.

To produce a cast of the invention bandage, the bandage is immersed inwater according to the usual pro- Further, the resin in the bandage isoptionally treated with a catalyst to' produce curing of the resin asrapidly as possible. This catalyst is conveniently added to the water inwhich the bandage is immersed. Catalyst concentrations in the water aremaintained at a value sufiicient to produce in the resin the desireddegree of cure in the desired interval of time. Catalyst concentrationsof 0.5 to 6.0% may be found to produce the desired effect. One indiciaof satisfactory environment for proper resin cure is pH, which ispreferably maintained at about 6 or below in order toetfect proper resincure within a short period of time at the relatively low temperaturewhich will prevail. ,Acidity control may be produced by use of theresin-curing catalysts, for example ammonium'chloride or'. other acidsalts 'or weak acids such as zinc sulfate, zinc chloride, aluminumsulfate, etc.

The following examples, in which parts are on a weight basis unlessotherwise specifically indicated, are presented not in a limiting sensebut as illustrating the invention.

Example I With parts of uncured water-soluble melamineformaldehyde resinprepared from a mixture of 1 mol melamine and 4 mols formaldehydeaccording to the foregoing procedure, there were mixed 90 parts of alphagypsum prepared substantially according to the procedure of U. S. P.1,901,051, and 40 parts water containing 0.5 part borax and 1.2 parts ofpolyvinyl acetate emulsion containing 55% polyvinyl acetate. The mixturehad the consistency of a thin paste. It was coated on gauze and driedfor about two minutes at 275 F. A strip of the dried bandage material 4inches wide by 5 yards long was dipped into a l /2% aqueous solution ofammonium chloride and wrapped around a cylindrical member to prepare acast. The cast was made of about 25 laminations of the gauze as measuredthrough its thickness. The cast was allowed to set for 24 hours at roomtemperature after which time it was tested for cast strength accordingto Federal specification GG-B-l07, June 21, 1951, section 4.3.6 (exceptthat setting time was 24 hours instead of 1 hour as called for by thespecification). Strength tests were also made on similar casts after 7days setting time. The result obtained is presented in the table below.

Example II A homogeneous mixture was prepared of parts ofmelamine-formaldehyde resin substantially the same as that employed inExample I, 85 parts of alpha gypsum and 35 parts water containing 0.4part boric acid, 0.8 parts 28% aqueous ammonia solution and 0.6 partpolyvinyl acetate emulsion containing 55% polyvinyl acetate.

I The paste was coated on gauze backing and dried. After preparing acast according to the procedure described in Example I, strength testswere carried out as described above. The results of tests for eaststrength are presented in the table below.

Example III A paste similar to that described in Examples I and II wasprepared using 25 parts aldehyde-triazine resin, 75 parts alpha gypsumand 45 parts water containing 0.6 part polyvinyl acetate emulsion, 0.4part boric acid and 0.59 part of 28% aqueous ammonia. The mixture wascoated on gauze and dried at 250 F. for about 3 minutes. A cast wasprepared as in Example I and tested as described in that example.Results are presented in the table below.

Example IV A paste similar to that described in the foregoing exampleswas prepared from parts alpha gypsum, 10 parts of the same resin and 50parts of aqueous ethyl alcohol containing 1 part of polyvinyl acetateemulsion. The mixture was coated on ordinary gauze and dried at F. for 2minutes. The cast was tested as in Example I, the results beingpresented in the table below.

Example V The slurry in this example was composed of 85 parts alphagypsum, 15 parts of the same resin and 2 parts of ammonium chloride,mixed with 60 parts of anhydrous methylene chloride containing 1 part ofpolyvinyl acetate emulsion. The mixture was spread on gauze using aknife coater, and dried at 100 F. for five minutes. A strip of thematerial 4 inches wide by 5 yards long was immersed in water, and a castwas prepared. The cast was tested according to the procedure describedabove with the results presented in the table below. For purpose ofcomparison the table also includes strength tests on a commerciallyavailable 4 inches wide by 5 yards long bandage made into a cast, thebandage being formed of alpha gypsum coated on and bonded to gauze, andhaving composition similar to invention bandages except that there wasno aldehyde-triazine resin present.

Cast Strength Pounds Example After 1 After 7 Day Days The invention isnot limited to the foregoing examples and description since there aremany modifications and equivalents within the scope of the invention.

The claims are:

1. A bandage for producing an immobilizing cast comprising a fabricbacking and bonded to said fabric a substantially dry compositioncomprising about 530% by weight of uncured aldehyde-triazine resin andabout 95 70% by weight of plaster of Paris based on the total weight ofresin and plaster of Paris, and sufiicient adhesive to bond saidcomposition to said backing.

2. A bandage for producing an immobilizing cast comprising a fabricbacking and bonded to said fabric a substantially dry compositioncomprising about 530% by weight of uncured melamine-formaldehyde resinand about 9570% by weight of plaster of Paris based on the total weightof resin and plaster of Paris, and suflicient adhesive to bond saidcomposition to said backing.

3. A bandage for producing an immobilizing cast comprising a wovenfabric backing and bonded to said fabric a substantially dry compositiencomprising about 10 7 15% by weight of uncured melamine-formaldehyderesin and about 90-85% by weight of plaster of Paris based on the totalweight of resin and plaster of Paris, sufiicient adhesive to bond saidcomposition to said backing, and plasticizer for said composition.

4. The method of producing a plaster of Paris bandage which comprisespreparing a paste of a liquid, plaster of Paris, and an uncuredaldehyde-triazine resin, the amount of resin being about -30% and theamount of plaster of Paris being about 95-70% of the combined weights ofresin and plaster of Paris, and sufficient adhesive to bond said resinand plaster of Paris to a Web, impregnating a web with said paste, anddrying the impregnated web under conditions to prevent substantialhydration of said plaster of Paris and to prevent substantial curing ofsaid resin.

5. The method of claim 4 for producing a plaster of Paris bandage whichcomprises preparing a paste of a liquid, plaster of Paris, an uncuredaldehyde-triazine resin, the amount of resin being about -15% and theamount of plaster of Paris being about 90-85% of the combined weights ofresin and plaster of Paris, impregnating a fibrous web with said paste,and drying the impregnated web under conditions to prevent substantialhydration of said plaster of Paris and to prevent substantial curing ofsaid resin, and sealing the dried material in a substantiallywatcr-impervious Wrapper promptly after said drying operation.

6. The method of claim 4 for producing a plaster of Paris bandage whichcomprises preparing a paste of an aqueous liquid, plaster of Paris, anuncured melamineformaldehyde resin, and retarder, the amount of resinbeing about 530% and the amount of plaster of Paris being about 95-70%of the combined weights of resin and plaster of Paris, impregnating afibrous web with said paste, and drying the impregnated web underconditions to prevent substantial hydration of said plaster of Paris andto prevent substantial curing of said resin.

7. The method of claim 4 for producing a plaster of Paris bandage whichcomprises preparing a paste of an aqueous liquid, plaster of Paris, anuncured melamineformaldehyde resin, retarder and plasticizer, the amountof resin being about 10l5% and the amount of plaster of Paris beingabout -85% of the combined weights of resin and plaster of Paris,impregnating a woven fibrous web with said paste, drying the impregnatedweb at temperature not above 300 F. for time short enough and underconditions to prevent substantial curing of said resin, and controllingthe pH of said bandage in the approximate range 7.0 to 10.0 during saiddrying operation.

8. The method of claim 4 for producing a plaster of Paris bandage whichcomprises preparing a paste of an aqueous liquid, plaster of Paris, anuncured melamineformaldehyde resin, retarder and plasticizer, the amountof resin being about 10-15% and the amount of plaster of Paris beingabout 90-85% of the combined weights of resin and plaster of Paris,impregnating a woven fibrous web with said paste, drying the impregnatedweb at temperature not above 300 F. for time short enough to preventsubstantial curing of said resin to volatile water content below about0.3% based on the weight of said resin, controlling the pH of saidbandage in the approximate range 7 to 10 during said drying operation,and sealing the dried material in a substantially waterimperviouswrapper promptly after said drying operation.

References Cited in the file of this patent UNITED STATES PATENTS2,419,440 Delmonte Apr. 22, 1947 2,557,083 Eberl June 19, 1951 2,571,343Dailey Oct. 16, 1951 OTHER REFERENCES The Lancet for Dec. 19, 1953, pp.1317-18.

1. A BANDAGE FOR PRODUCING AN IMMOBILIZING CAST COMPRISING A FABRICBACKING AND BONDED TO SAID FABRIC A SUBSTANTIALLY DRY COMPOSITIONCOMPRISING ABOUT 5-30% BY WEIGHT OF UNCURED ALDEHYDE-TRIAZINE RESIN ANDABOUT 9570% BY WEIGHT OF PLASTER OF PARIS BASED ON THE TOTAL WEIGHT OFRESIN AND PLASTER OF PARIS, AND SUFFICIENT ADHESIVE TO BOND SAIDCOMPOSITION TO SAID BACKING.